1. Field of the Invention
The present invention relates to a liquid crystal display device. In particular, the present invention relates to a liquid crystal display device having a shift register formed by using a transistor. In addition, the present invention relates to a method for driving the liquid crystal display device. Further, the present invention relates to an electronic device having the liquid crystal display device in a display portion.
2. Description of the Related Art
In recent years, with the increase of large display devices such as liquid crystal televisions, liquid crystal display devices have been actively developed. In particular, a technique for forming a pixel circuit and a driver circuit including a shift register or the like (hereinafter also referred to as an internal circuit) over the same insulating substrate by using transistors formed of a non-crystalline semiconductor (hereinafter also referred to as amorphous silicon) has been actively developed, because the technique greatly contributes to low power consumption and low cost. The internal circuit formed over the insulating substrate is connected to a controller IC or the like (hereinafter also referred to as an external circuit) through an FPC or the like, and its operation is controlled.
A shift register which is formed by using transistors formed of a non-crystalline semiconductor has been devised among the above-described internal circuits (for example, see Reference 1: Japanese Translation of PCT International Application No. H10-500243). Since in a shift register disclosed in Reference 1, a period in which an output terminal is in a floating state is long, there has been a problem in that noise easily occurs in an output signal of the shift register. In order to solve the problem of the shift register disclosed in Reference 1, a structure of a shift register in which an output terminal does not get into a floating state has been devised (for example, see Reference 2: 2.0 inch a-Si:H TFT-LCD with Low Noise Integrated Gate Driver SID '05 DIGEST pp. 942 to 945).